The invention relates to an electric-motor-driven housing for a feed pump, in particular for a feeding device for fuel, as generically defined by the preamble to the main claim.
In such feeding devices, the fuel is pumped from a fuel tank, for instance to an injection system of the internal combustion engine of a motor vehicle. One such feeding device is known from German Patent Disclosure DE 44 44 854 A1, in which the feed pump is driven by an electric motor. In these arrangements, it is important that no electrical discharge events, which can cause ignition of the fuel or of the fuel-air mixture in the tank, occur. The corresponding diversion of electrostatic discharges is difficult to achieve in components that for the most part, for engineering reasons, are made from plastic and are electrically only poor conductors or even nonconductors.
The direct current electric motor of the known feed pump is typically also closed on the commutator side by a connection cap of nonconductive plastic, with a surface resistance of greater than 1014 ohms, and thus cannot be used to divert electrostatic discharge to the ground potential of the feeding device, nor can it shield against electromagnetic radiation, for instance in the high-frequency range. Another possibility is that the housing of the feed pump could be applied to ground potential by means of an additional contact baffle, but no shielding action at the connection cap can be achieved by making this provision. A fully conductive cap would entail excessive expense in this respect.
The housing described at the outset for a feed pump driven by an electric motor, in particular for a feeding device for fuel, is advantageously refined with the characteristics of the body of claim 1, in which the connection cap on the commutator side, on which the electrical connection contacts and pump inlets and/or outlets are mounted, is made from an electrically conductive plastic. Via an electrically conductive connection, a connection with a ground potential can then be made in a simple way.
The surface resistance of the connection cap is selected according to the invention such that a diversion of electrostatic discharge to the ground potential is assured at little engineering effort or expense. Thus shielding against electromagnetic radiation in the high-frequency range can be accomplished as well, in a simple way. Since for production it is advantageous if the electrical connection contacts rest directly on the connection cap, without any further insulation, it can be assured by means of a correct choice of the surface resistance that a predeterminable short-circuit current, for instance approximately 0.1 A, between the connection contacts is not exceeded. The surface resistance of the connection cap is preferably in the range of 104 ohms.
According to the invention, the connection cap can have an electrical contact over the entire surface or at a plurality of points on the circumference with the further electrically conductive parts of the housing of the feed pump or of the electric motor, in order to improve the shielding and diversion still more. The conductive plastic of the connection cap can for instance be a polyamide or polyoxymethylene provided with conductive metal or carbon fibers.
These and further characteristics of preferred refinements of the invention are disclosed not only in the claims but also in the description and the drawings; the individual characteristics can each independently or in groups be used to make subsidiary combinations in the embodiment of the invention and in other fields and can represent both advantageous and independently patentable embodiments for which patent protection is claimed here